Preform, apparatus, and methods for casing and/or lining a cylindrical volume

ABSTRACT

According to the invention, the tubular preform is radially deformable between a longitudinally folded state and substantially cylindrical unfolded state to form a length of rigid tube in situ. The preform comprises a flexible and watertight inner envelope (6) whose peripheral extent is equal to the internal extent of the length of tube, and, formed on the outside of said inner envelope, reinforcement (2) made of filamentary structure comprising a plurality of fibers impregnated with a settable resin, including fibers (3) oriented mainly in the peripheral direction of the preform, each of these fibers (3) extending over more than one turn and co-operating with adjacent fibers by making contact therewith such that adjacent fibers can slide over one another while the preform is in any state other than its unfolded state where, under internal pressure, the fibers are locked together by the friction between them due to a capstan effect.

The invention relates to apparatuses and methods for making a tube insitu from a folded preform that is easier to handle and install than arelengths of rigid tube.

BACKGROUND OF THE INVENTION

There are several applications that require tubes to be made and used onsite. One such application is casing boreholes, in particular in the oilindustry; a second is making ducting of great length such as submarinepipelines, and finally another consists in restoring or lining buriedpipelines or casing.

The purpose of a borehole, in particular an oil exploration borehole, isto establish a passage for communication between the surface and anobjective underground. For most wells, the initial diameter of the boreis large, whereas once the well is completed, the final communicationpassage is of small diameter: usually less than 6" (152 mm). The passageis then of constant diameter equal to this small final diameter up theentire height of the well.

To establish such communication while withstanding the pressuresencountered, longer and longer successive concentric lengths of casingare lowered and suspended from the surface and are then cemented inplace. Given that each length of casing must pass through the precedinglength, its outside diameter must be less than the inside diameter ofthe preceding length, and to obtain a final access diameter of 4" to 8"(102 mm to 203 mm), it is necessary to begin with a borehole of largediameter, in particular 171/2" (445 mm), and even 36" and 26" (915 mmand 660 ram) for offshore boreholes.

Present methods thus require an initial hole of large diameter to bedrilled in order to have a sufficient number of lengths of casingavailable for making the well. The direct consequences of this techniqueare that the time required for drilling is long and consumables (steeltubes, drilling mud, sealing cement, etc . . . ) are needed in largequantities. In addition, because the initial lengths of casing are oflarge diameter, their wall thicknesses are limited for reasons ofweight. The capacity of such initial lengths of casing to withstand highinternal pressures is therefore limited. It is necessary for eachfollowing inner tube to be suspended from the surface in order toincrease the ability of the top portion of the casing to withstand thehigh pressures that obtain at the bottom of the well.

In addition to the large quantity of consumables, and the long timerequired by said operations of drilling and installing concentriccasing, present techniques suffer from other drawbacks. Cementing isdifficult to perform because of the narrowness of the annular space andthe hazards of the terrain drilled through. In addition, the fact thatthe casing is made of metal constitutes an obstacle to performingvarious measurements, in particular electrical measurements, that arerequired for locating productive layers for the future purpose ofputting the hydrocarbon reserves into production.

There thus exists a need to simplify the operations of drilling and ofcasing.

In addition, it is difficult and lengthy to install pipework, inparticular offshore and in particular when of relatively large diameter,because of the need for a plurality of lengths of steel tube that makeup the pipework to be interconnected end-to-end, generally by welding,and for said pipework to be paid out progressively from the vessel onwhich it is assembled while it is being assembled and without kinkingit, thereby giving rise to high tensions during laying. There is also aneed to make the laying of such pipework easier, particularly in deepwater and/or if the pipework is large in diameter.

Finally, restoring or lining underground casing or pipework implies thatan inner lining must be installed in a faulty pipe (that has becomeporous or unsealed when lengths are connected together), said liningbeing capable, at least in some locations, of replacing the pipeworkitself which may have completely disappeared due to corrosion.

The present invention seeks to satisfy these needs by making it possiblewhen applied to a borehole to retain a small drilling diameter over theentire length of the well together with small diameter casing. Whenapplied to making offshore pipework, the invention enables the pipeworkto be installed while flat, thereby reducing the minimum acceptableradius of curvature during laying and consequently reducing tensionduring laying; and when applied to repairing faulty pipework, thefunction of the preform is to consolidate the pipework and sometimeseven to take its place. These results are obtained by using a deformableand settable composite material of minimum radial size prior to settingand possessing a structure that enables it to be folded into itsminimum-size state and to be radially inextensible even before settingso as to enable it to take up its final shape even in the absence of anyoutside restraint.

SUMMARY OF THE INVENTION

To this end, in a first aspect, the present invention provides a tubularpreform that is radially deformable between a longitudinally foldedstate and a substantially cylindrical unfolded state to form a length ofrigid tube in situ, the preform comprising a flexible and watertightinner envelope whose peripheral extent is equal to the internal extentof the length of tube, and, formed on the outside of said innerenvelope, reinforcement made of a filamentary structure comprising aplurality of fibers impregnated with a settable resin, including fibersoriented mainly in the peripheral direction of the preform, each ofthese fibers extending over more than one turn and co-operating withadjacent fibers by making contact therewith such that adjacent fiberscan slide over one another while the preform is in any state other thanits unfolded state where, under internal pressure, the fibers are lockedtogether by the friction between them due to a capstan effect.

This structure allows the preform to be "folded" lengthwise even thoughit has a thick wall, while nevertheless avoiding unacceptable bendingstresses in said wall or needing to use materials that are veryresilient and which as a result do not possess the mechanicalcharacteristics required for making a tube that can withstand highpressures.

For example, a polymerized composite wall, i.e. in which the reinforcingfibers are held in place relative to one another within a rigid matrix,can achieve a radius of curvature of less than 20 mm elastically only ifits thickness is less than 5/10-ths of a millimeter. A thick wall in themeaning of the invention is thus a wall whose thickness is greater than5/10-ths of a millimeter since the smallest radius of curvature thatwill be required in applications of the invention is about 20millimeters.

Such folding is made possibly only because the filamentary structureconstituting the reinforcement of the tube includes elements that arecapable of sliding relative to one another in the matrix while in itsinitial, fluid state. The term "filamentary structure" should beunderstood as meaning a structure including threads of syntheticmaterial, or of metal in certain applications, which may be woven orcollected together in rovings wound to form the wall of the tube, havingone or more layers, and having determined crossing angles. The maincharacteristic of this structure lies in the presence of a large numberof circumferential threads such that the structure is practicallyinextensible in the circumferential direction under the effect of agiven internal pressure because of the mutual friction between thecircumferential threads (capstan effect) which locks them together.

In a first embodiment, the filamentary structure is constituted by aplurality of long fibers impregnated with settable resin wound onto theinner envelope while supported by a mandrel and covered with sheets oflongitudinal fibers.

In another embodiment, the filamentary structure comprises a pluralityof concentric sleeves placed one within another, each of the sleeveshaving a determined peripheral size under load that is slightly greaterthan the size of the sleeve that it surrounds or slightly smaller thanthe size of the sleeve which surrounds it, thereby forming a compactstructure.

In another embodiment, for applications where it is important for theminimum weight of the preform to be high, for example for ensuring thatsubmarine pipework is stable, the filamentary winding may advantageouslybe constituted entirely or partially of metal wires of small section(about 1/10 mm).

The preform of the invention preferably also includes a flexiblewatertight outer envelope whose peripheral size is equal to the outsidesize of the length of tube, with the reinforcement being confinedbetween the two envelopes.

Each length of flexible preform includes a flexible end wall connectedin watertight manner to one of the ends of the tubular wall, and at theopposite end it includes a second flexible end wall having a filler ductfor filling the tubular section passing therethrough, which duct isconnected to a source of fluid for causing the preform to take up acylindrical state starting from a folded state in which its insidevolume is isolated from the outside or is even kept evacuated. Thepreform finished off in this way is ready for hydraulic testing in thefactory prior to being stored folded under a vacuum and on a transportdrum. The vacuum maintained inside the preform stiffens the foldedpreform and keeps it at a constant volume, and thus at a constantbuoyancy while the length is being immersed in a fluid, and in spite ofvariations in the hydrostatic pressure of the surrounding liquid.

In a variant embodiment, the wall of the preform may include a thicklayer or core sandwiched between two pluralities of filamentary windingsfor the purpose of withstanding transverse compression and sufficientlyflexible to be suitable for folding, thereby increasing the secondmoment of area of the tubular section. In some cases, the core could bemade of a material of high density in order to increase the weight ofthe length of flexible preform. It is also possible to provide a coreconstituted by winding thin impregnated foils capable of slidingrelative to one another so as to facilitate radial folding and which aresubsequently prevented from sliding by the impregnating resin setting.

In the folded state, the preform has its wall flattened against itself,and the longitudinal edges thereof form hairpin bends around respectivevolumes filled with incompressible material that is semi-solid atambient temperature, limiting the radius of curvature of the fold. Insome cases, the material is also of high density, achieved by using amineral filler, thereby increasing the mass of the length and making iteasier to sink in a liquid medium. All or part of this material may bereplaced by tubular ducts whose role is explained below, which ductsconstitute elements that limit the radius of curvature of the wall ofthe preform.

Depending on the purpose of the preform: making pipework, casing aborehole, etc . . . , the preform is presented in the folded stateeither in the form of a substantially flat strip or else in the form ofa horseshoe, with the two hairpin bends being adjacent to each other. Inthe horseshoe configuration, the overall radial dimensions of thepreform are smaller than the inside diameter of the preform in itsunfolded state.

Advantageously, the space inside the horseshoe constitutes a housing formaterial in the plastic state for use in making a watertight bondbetween the wall of the tube obtained by unfolding and hardening thepreform and the ground it passes through when the invention is used forcasing a borehole, particularly in the oil industry.

The length of preform and sealant are contained in an elastic envelopewhose peripheral size at rest is substantially equal to the outsideperipheral size of the preform in the unfolded state.

In the event that it is desirable for the casing to have a single insidediameter and simultaneously for there to be a sealing overlap betweentwo successive lengths, the end of the length of preform furthest fromthe end through which the filler duct passes has an inside diameter inthe unfolded state which is equal to the outside diameter of its otherend, over portions of substantially equal length.

Advantageously, to enable the casing to be filled progressively from thebottom upwards, the filler duct extends inside the length of preform tothe vicinity of the opposite end wall. More precisely, this duct may besplit into two branches extending parallel to each other in each of thevolumes filled with the above-mentioned incompressible material andconstituted by the above-mentioned tubes for limiting curvature, withthe walls of these tubes being connected at least in part to the endwall of the length of preform so as to constitute the means forextracting said end wall after the sealant and the preform wall haveset.

To ensure that filling takes place progressively from the bottomupwards, a plurality of bands are disposed at intervals along the casingand they break one after another as filling takes place. This avoids anyrisk of uncontrolled filling that could leave a poorly filled and thusnon-cylindrical neck between two portions each inflated to the nominaldiameter.

The invention also provides a method of casing a borehole using theabove apparatus, which method comprises the following steps:

(a) drilling a portion of borehole to a diameter substantially equal tothe outside diameter of the casing;

(b) lowering the section of folded flexible preform inside the boreholeand/or the previously installed casing, and than when substantially theentire length of said section of folded flexible preform is receivedbeyond the bottom portion of the previously installed casing, filling itwith a fluid to cause it to take up its cylindrical state, starting fromthe bottom;

(c) allowing setting to take place of the matrix impregnating thefilamentary structure which is tensioned by the internal fillingpressure; and

(d) raising the filling duct.

To provide sealing between two successive lengths, the method of theinvention may include the following steps:

(a) drilling a portion of borehole to a diameter substantially equal tothe outside diameter of the casing;

(b) lowering the flexible preform section in its folded state inside thepreviously installed casing and stopping the descent of the foldedpreform section so that the top portion of the preform remains receivedinside the previously installed portion of casing whose inside diameteris equal to the outside diameter of the top portion of the preform;

(c) filling the preform to take it from its folded state to itscylindrical state, starting from its bottom end;

(d) allowing setting to take place of the matrix impregnating thefilamentary structure which is tensioned by the internal fillingpressure; and

(e) raising the filling duct.

In a variant embodiment, the preform of the invention is closed at bothends and in its folded, first state its maximum outside radial size isless than its inside diameter achieved when in an unfolded, secondstate, and it possesses at least one flow duct which extends axiallyinside the preform and which passes in sealed manner through its closedends, means existing for connecting the inside volume of the preform toa source of fluid to cause it to pass from its first state to its secondstate by being inflated. The flow duct serves to cause a cement slurryto flow in the annular space that exists between the borehole and thepreform lowered down the borehole, whether it has been unfolded or not.In this variant embodiment, no sealant is carried by the preform.

In a first embodiment, the means for connecting the preform to a sourceof filler fluid is constituted by a separate duct connecting the insidevolume of the preform to the source.

In another embodiment, said connection means is constituted by a branchon the flow duct and connected thereto via a conventional branchcoupling sleeve situated in the vicinity of the top of the preform. Inboth cases the flow duct and the inflation duct are advantageouslyconstituted by pipes received in the preform and serving to limit theradius of curvature of its wall.

The preform may also include a diaphragm splitting its inside volumeinto two superposed volumes, one of which is shorter than the other.

The end of the longer volume that is further from the other volumepossesses a portion whose length is not less than the length of saidother volume and whose inside diameter is substantially equal to theoutside diameter of said other volume when they are both in their secondstate.

Each of the volumes is fitted with independent means connecting it to asource of fluid under pressure.

The diaphragm is breakable beyond a pressure threshold.

In addition, the said flow duct includes a cementing non-return valvepreventing fluid returning towards the source, said valve being made ofdrillable materials, and there exists a disconnection zone situatedinside the section of flexible casing close to one of its ends.

Finally, it should be observed that the cement may be caused to flowwhen the preform is still in the folded state. Under such circumstances,provision is made to inflate or fill the preform and/or each of itscompartments from the bottom upwards so that inflation causes the cementto be expelled upwards along the borehole since that is the onlydirection from which it can be removed.

The invention also provides another method of casing a borehole usingthe above cement-flow apparatus, the method comprising the followingsteps:

(a) drilling a portion of borehole having a diameter substantially equalto the outside diameter of the casing;

(b) lowering the section of flexible preform in its folded state downthe previously installed casing and stopping descent of the foldedsection of preform so that the top portion of the preform remainsreceived in the previously installed portion of casing which has aninside diameter equal to the outside diameter of the top portion of thepreform;

(c) causing a cement slurry to flow via the flow duct so that the slurryrises up the annular space between the folded section of preform and thewall of the borehole;

(f) filling the section of preform from the bottom with a fluid fortaking said section of preform to its second state;

(g) allowing the cement slurry and the preform to set, thereby sealingthe casing made in this way in watertight manner to the wall of theborehole; and

(h) detaching and raising the flow duct.

Other advantages and characteristics of the invention appear from thefollowing description of embodiments of the invention given by way ofnon-limiting example and shown in the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic cross-section through a borehole showing asection of preform in the folded state being lowered inside a section ofcasing that has previously been installed;

FIG. 1B is a diagrammatic cross-section through a larger section ofplastic sealant;

FIG. 2 is a diagrammatic view of a flattened configuration of thepreform disposed in successive layers on a drum;

FIG. 3A is a diagrammatic perspective view of the structure of oneembodiment of the wall of a length of casing of the invention in itscylindrical state;

FIG. 3B is a diagrammatic perspective view of the structure of the sameembodiment of the wall of a length of casing in its cylindrical statewhen said structure is pressed firmly against the inside of existingcasing for the purpose of lining it;

FIG. 4 is a diagrammatic vertical section through the end of a sectionof casing after it has been installed and also showing a section ofcasing being lowered in its folded state;

FIG. 5 is a diagrammatic vertical section through a section of casing inits cylindrical state after it has been filled;

FIG. 6 is a vertical section through a second embodiment of successiveconcentric lengths of casing in a borehole cased in accordance with theinvention after the casing has been filled;

FIG. 7 shows the cased borehole of FIG. 6 after the preform and thesealant have been put into place and after the filler endpiece has beenremoved;

FIG. 8 is a diagrammatic vertical section through a borehole showing thepreform of the invention as filled after it has been lowered down theborehole below the preceding length of casing;

FIG. 9 is a diagrammatic cross-section through the borehole showing thelongitudinally folded apparatus while under a vacuum having a generallyoval shape and while being lowered through previously cemented casing;

FIG. 10 is a diagrammatic cross-section through the borehole shown inFIG. 8;

FIG. 11 is a diagrammatic vertical section through a borehole showing alength of casing having two separate and unequal volumes, the shortervolume still being in the folded state; and

FIG. 12 is a diagrammatic vertical section through the borehole of FIG.11 after the shorter volume has been filled.

DETAILED DESCRIPTION OF THE INVENTION

In FIGS. 1A and 4 to 7, there can be seen a borehole 1 provided withcasing 2 in accordance with the invention, i.e. made of a compositematerial that has become rigid by the matrix impregnating itsfilamentary structure setting, either by polymerization or by settingunder the effect of heat from the borehole or from a flow of hot fluid,or finally by putting a hardener into contact with the impregnatingresin.

The wall of this casing is thick in the sense used in the presentinvention, i.e. once polymerized it cannot take up a radius of curvatureof less than 40 mm elastically.

The filamentary structure of this wall is very special. It possesses,between an inner skin and an outer skin, a plurality of fibers whosemain orientation is circumferential (or peripheral) so as to be good forwithstanding a high internal pressure, said fibers also being capable ofsliding relative to one another in the circumferential direction so thatsaid thick wall is capable of being folded while avoiding unacceptabletraction and bending stresses being applied to certain fibers in thewall which would otherwise happen if the fibers were prevented fromsliding longitudinally relative to one another.

It is also necessary, once the structure had reached its unfolded size,for the fibers to be prevented from moving relative to one another sothat the structure is radially inextensible under the effect of internalpressure. This feature of inextensibility must be obtained before theresin sets since setting is solely to ensure that the structure remainsin its unfolded state, i.e. setting does not contribute to withstandinginternal pressure. The purpose of setting the resin is essentially toprevent the structure from buckling under the effect of externalpressure, with its shear strength that prevents the fibers from slidingrelative to one another being satisfactory. The fibers are mutuallylocked together by the friction that develops between each fiber and theadjacent fibers along a line of contact that is long enough for acapstan effect to be produced. This effect exists so long as each of thefibers that is oriented mainly circumferentially occupies at least oneturn, and preferably occupies a plurality of turns.

There are several ways in which a filamentary structure possessing thesecharacteristics can be made. One such way is illustrated in FIG. 3A andit consists in winding long fiber rovings 4 that are preimpregnated withresin onto a mandrel that has previously been covered with an envelope 6that is flexible and watertight, the thickness to which the rovings arewound being defined by the difference in diameter between the insideenvelope 6 and an outside envelope 7 that is also flexible andwatertight and which covers the winding made in this way, therebyretaining dimensional uniformity (thickness) along the entire structure.It is preferable to install a sheet of longitudinal fibers 5 woven withfilaments 5' between the inside envelope 6 and the winding 4 so as toenable the preform to withstand longitudinal stresses that result fromits weight and from pressure being applied to its ends. If it isnecessary for the preform to have some minimum weight, for example toensure that it sinks in a mud of high density, then some or all of thesynthetic fibers may be replaced by steel wires.

A second technique consists in making the filamentary reinforcement froma strip of material by winding the material helically on a mandrel so asto produce continuous reinforcement. Such a strip is special in that ithas one longitudinal edge that is longer than the other. It is thuspossible to obtain a multilayer wall with each layer extending from theinside surface of the reinforcement to the outside surface thereof.

In another embodiment, the wall of the casing is constituted by aplurality of sleeves 3. The sleeves may be made in several differentways. For example, each of the sleeves may essentially comprisecircumferential filamentary windings 4 woven with longitudinal threads 5as shown in FIGS. 3. It is also possible to weave such sleevesconventionally or to make them by adhesively superposing a plurality ofsheets of threads that are appropriately oriented relative to thelongitudinal axis of the preform. It is also be possible to braid suchsheets or to weave them as a tubular sock. The thread which may be aglass fiber thread or a metal wire thread, for example, and the way inwhich it is made up should be chosen so that the sleeves 3 arepractically inextensible, e.g. under the effect of internal pressure.The wall comprises a plurality of sleeves threaded in one another, witheach sleeve having a peripheral size that is slightly greater thanand/or slightly less than the size of each adjacent sleeve.

The set of sleeves is received between an inside envelope 6 and anoutside envelope 7 that are flexible and waterproof and that define thethickness of the wall of the casing.

Within these envelopes, the filamentary sleeves are impregnated with amatrix of the kind constituted by a polymerizable or a thermosettingresin of conventional materials, such that it remains fluid at ambienttemperature so that the wall of the preform can be folded and placed inone of its folded states as shown in the center of FIG. 1A, in FIG. 1B,and in FIG. 2. During said folding, and during any subsequent unfolding,the sleeves can slide peripherally over one another because the resinwith which they are impregnated is still fluid.

At least two types of folding can be performed: horseshoe folding 17 asshown in FIGS. 1A and 1B; and flat folding 15 as shown in FIG. 2. In thecase shown in FIGS. 1A and 1B, the folding is specific to a casingapplication in which the radial dimensions of the folded preform areless than its inside diameter when in the unfolded state. The flatfolding 15 rolled up on a drum 16 as shown in FIG. 2 relates to apreform for making pipework, with the flat surface providing minimumresistance to bending in its thin direction.

Two radius of curvature limiters or shapers 8 and 9 are received insidethe tube at locations where the wall of the tube is folded back ontoitself around hairpin bends. The purpose of these shapers is to limitthe radius of curvature in locations where the wall of the preform isfolded back onto itself. The material used for these shapers is of atype that is semi-solid at ordinary temperature. In preferredembodiments of the invention, each shaper is enclosed in a flexiblesheath 11, and 12 whose function during filling is explained below (FIG.1A) or it is constituted by tubular ducts 11' and 12' (FIG. 1B) whichare optionally filled with semi-solid material which also serves asballast. The material used becomes fluid under the effect of an increasein temperature such that it can be removed by a flow of fluid when aflow is established inside the preform during filling thereof, or,optionally, when cement is made to flow.

During flattening and folding of the preform, the air that was inside itis expelled, and the vacuum created in this way constitutes means forholding the wall in its folded state. The points referenced A and B inFIG. 1A show how the sleeves slide relative to one another when the tubepasses from its folded state to its cylindrical state.

In the case shown in FIGS. 1A and 1B, the preform is not only flattened,but is also curved so that its two hairpin bend ends are brought fairlyclose to each other, thereby defining a volume of some size between thebranches of the horseshoe shape. A kind of sausage 13 of semi-solidmaterial is placed between the branches of the horseshoe shape, therebymaking it possible to provide watertight binding between the outsidewall of the casing and the terrain it passes through. This material mayalso be of the polymerizable type, or of the thermosetting type, whileremaining plastic at ordinary temperature and becoming fluid at a highertemperature when the preform is put into its cylindrical state (whichhigher temperature may be the temperature of the borehole or thetemperature of the fluid used for filling the casing). It is alsopossible to provide a material that retains a certain amount of residualelasticity when in its final state whereby the join between the casingand the terrain is improved.

The wall of the tube of the invention finally includes a stretchableoutside skin 14. This skin surrounds the tube in its folded statetogether with the sealant housed between the branches of the horseshoeshape, and its peripheral size is substantially equal to the outsidesize of the casing. When the preform is in its cylindrical state, theskin 14 fits over the outline of the terrain, as shown in FIG. 1, andthe sealant 13 completely fills the residual volume that remains betweenthe outside surface of the tube and the hole bored through the terrain.

In FIGS. 3A and 3B, in addition to the items described above, there canbe seen a core 18 inside the wall of the casing, which core isconstituted by a flexible foil that stands up well to transversecompression so as to increase the second moment of area of the wall, orelse, for the purpose of making the casing heavier while still allowingit to be folded, it comprises a laminated structure of thin foils thatare wound on one another and impregnated with resin.

There is ample explanation above that one of the characteristics of theinvention results from the capstan effect due to the friction betweenthe circumferentially-oriented fibers when the preform is inflated. Whenthe invention is applied to lining existing pipework, for the purpose ofreplacing the pipework at locations where it is missing, inflating thepreform must cause the preform to be pressed against the existingpipework before the capstan effect is allowed to take place. Undercircumstances, the circumferential fibers subjected to externalretention of the tube 2' to be lined and to the force of the internalinflation pressure tend to undulate slightly in the longitudinaldirection of the preform as shown at 4' in FIG. 3B, thereby slightlyincreasing the thickness of the preform. The lining is thus a littlethicker in regions where it presses against a tube than it is in regionswhere it replaces the tube. It can thus be seen that the thick structureof the invention lends itself very well to repairing tubes, and betterthan apparatus designed exclusively for internal lining since suchapparatus cannot replace the missing portions of a tube. Finally, theability of the circumferential fibers to take up excess length due to asmaller diameter than that of the preform after inflation merely byundulating allows the preform to conform to tubes to be repaired havinga range of diameters due to slack manufacturing tolerances.

FIG. 4 is a section through a folded tubular preform of the inventionwhile being lowered down a borehole 1. Bands 30 are disposed around thefolded preform along its length. It is thus ensured that the preform isfilled from the bottom upwards since fluid is injected via the bottomend of the preform and as filling takes place to bands 30 are broken inturn since their breaking strength is designed for this purpose. In FIG.5, the section is kept in its cylindrical state and in addition to thewall 3, it comprises two end walls 19 and 20 which close the insidevolume of said tubular section. The top end wall 19 is connected to thewall by conventional means, in particular such as described in Frenchpatent application No. 90 08474 filed Jul. 4, 1990, and it has a duct 21passing in sealed manner therethrough whereby a filler fluid can beinjected into the tubular section. The duct 21 is connected to the twopipes 11 and 12 which contain the material 8 and 9 for limiting theradius of curvature.

The bottom end wall is connected to the tubular wall 3 via a protectivesleeve 22 and it is also secured to the bottom portions of the pipes 11and 12 in order to enable it to be recovered.

It may be observed in FIG. 5 that the bottom end 3a of the wall 3 hasinside and outside diameters that are slightly larger than over theremainder of its length. In addition, the top portion 3b thereof is ofslightly smaller thickness than the normal section of the wall so thatits outside diameter is equal to the inside diameter of the bottom end3a of the preceding section of casing, and so that its inside diameteris equal to the inside diameter of the normal section. Successivesections can thus overlap with the top end of one bearing, on filling,against the inside surface of the bottom end of the previously installedsection which is now rigid. Naturally, the borehole that is designed toreceive such casing includes an end which is drilled using a hole openeror reamer to enable said enlarged portion of the casing to expand whenthe casing is filled.

The above-described sleeve 22 is intended to protect said bottom contactsurface when drilling continues after a preceding section has been casedagainst abrasion and shock from the drilling tool (see FIG. 5). Thissleeve may be removable, i.e. it does not set like the wall 3 and sinceit remains flexible to some extent and is capable of being Grasped byits bottom end and pulled up through the inside of the casing 3 prior tothe following section of casing being lowered.

FIG. 5 shows that a section of casing is made from a plurality oflengths put end to end by means of joints 23. This embodiment makes itpossible to adjust the length of the casing to the length required onsite and it facilitates manufacture and hydraulic testing of sections ofcasing.

It may also be observed that it is possible to adjust the quantity ofsealant as a function in particular of the nature of the terrain drilledthrough, by adjusting the section of the sausage installed in the hollowof the folded preform (rock drilled to the outside diameter of thecasing will require relatively little sealant, whereas softer terrainwhich is subjected to erosion during drilling will require more).

A section of drilled borehole is thus cased by lowering a length ofcasing down the borehole while the casing is in its folded state. Onceput into place in this way, heat due to the temperature of thesurrounding terrain or due to a flow of hot fluid causes the material 8and 9 in the radius of curvature limiters to become fluid. This materialcan then be expelled into the inside of the casing under drive fromfluid injected via the duct 21. The casing thus begins to fill and takeup its cylindrical state. The sausage 13 of sealant is compressedbetween the wall 3 and the borehole 1 and is thus pushed backcircumferentially to fill up the interstices between the boreholedrilled through the terrain and the outside wall of the casing. Thecasing is thus pressed progressively against the inside wall of theborehole starting at the bottom and moving upwards, and its top end ispressed against the inside surface of the preceding section of casing.If there is any excess sealant, it is squeezed into the precedingcasing. Thereafter the wall 3 is caused to set, e.g. by circulating ahot fluid at an appropriate temperature (or by waiting for setting tooccur naturally over a period of time because of the downholetemperature or because of any other conventional means), after which thetop end wall 19, the pipes 11 and 12, and the bottom end wall areremoved by withdrawing the duct 21. The protective sleeve 22 remains inplace. It is then possible to drill the next section of the borehole.

FIGS. 6 and 7 show an alternative embodiment of the invention. Unlikethe preceding examples, instead of making the casing using casing of asingle diameter, which requires connection zones to be made byperforming drilling operations with a reamer having two differentdiameters, the casing is performed in the manner that is conventionalfor lengths of steel casing, by drilling successive lengths of boreholeat different diameters without reaming, and casing each length withcasing that is likewise of a different diameter (e.g. casing tubes 24and 25 of FIGS. 6 and 7). For example, under such circumstances, it ispossible for a final diameter of 7" (178 mm) to replace a program ofsteel casing having diameters 20", 133/8", 95/8", and 7" (510 mm, 340mm, 245 mm, and 178 mm) with a program of casing of the invention havingdiameters 10", 9", 8", and 7" (255 mm, 229 mm, 203 mm, and 178 mm), withthe thickness of each casing wall being 1/2". Because of the invention,there is no longer any need to leave an annular space for a flow ofcement around the casing. This casing capable of being lowered while inthe folded state may have an outside diameter that is equal to theinside diameter of the preceding casing. This makes it possible to omitenlarged regions. In addition, the length of the casing and theinstallation position are no longer as critical as before since theamount of overlap can be chosen freely.

FIG. 6 shows that each section of casing 25 of a given diameter is infact greatly simplified. To enable it to be filled and passed to thecylindrical state starting from the bottom and moving upwards, a liquid26 of density greater than the liquid filling the borehole is injectedvia the tube 27 which constitutes one of the curvature limiters. Theother curvature limiter is constituted by a pipe 28 that allowscirculation to take place along the well.

FIG. 7 shows the section of casing during the stage of testing thebottom shoe after the top end wall has been removed together with thetube 21, i.e. after the wall has set.

The preform of the invention may also be used for making up anotherapparatus for casing a borehole that is slightly different from thatdescribed above and that is implemented by a method that is alsodifferent.

In FIG. 8, a borehole 51 is drilled through preceding casing 52 which iscemented to the previous borehole 51' by cement 53. The preceding casing52 may either conventional steel casing if it is the first casing, or itmay be casing of the invention. Steel casing is constituted by tubularlengths that are about 12 meters long and of constant diameter and thatare assembled together by screw connectors to form casing of the desiredlength. The section of casing 54 of the invention is closed at its topend or head 55 and at its bottom end 56 and it is lowered down theborehole by means of a circulation duct 57 which includes an open bottomend 58 passing through the bottom end wall of the tubing 56. Aninflation duct 59 is connected to the head 55 of said length of tubing54.

In a variant embodiment (not shown) the inflation pipework is connectedas a branch on the circulation duct. This branch is preferably connectedto the circulation duct in its portion inside the section of casing 54or in the immediate (outside) vicinity of the head of the section oftubing by means of a branch coupling sleeve opening the branch andsimultaneously closing the circulation duct, or closing the branch andkeeping the duct 57 open. The duct 57 is consequently selectivelyconnected to a source of inflation liquid or to a source of sealantfluid depending on whether the casing is to be inflated or cemented.

In FIG. 9, the section of tubing 54 is shown in a first state, with itsinside volume 60 being evacuated, such that the radial dimension of thissection of casing 54 is less than the inside diameter of the precedingcasing 52, i.e. less than the inside diameter of the casing 54 of theinvention when in its second state of maximum radial size after itsinside volume 60 has been filled. When the section of casing 54 hasreached its installation position (i.e. when its top end 55 is situatedbeneath the bottom end of the preceding casing 52), the volume 60 isinflated by being filled via the inflation pipework 59 which isconnected to a source of liquid under pressure (not shown).

FIG. 10 shows the section of casing 54 in section while it is in itssecond state, i.e. when inflated. Its outside diameter is greater thanthe inside diameter of the preceding casing 52. At this moment, a cementslurry is injected through the circulation duct 57 and it fills theannular gap 61 between the casing and the borehole.

In FIGS. 11 and 12, there can be seen an advantageous variant embodimentof the invention in which the section of casing includes an internaldiaphragm 63 splitting its inside volume into two volumes: a long lowermain volume 64 and a short upper small volume 65. The two volumes haveindependent inflation ducts 66 and 67. The bottom portion 18 of the wallof the section of casing delimiting the volume 14 is of larger diameterthan the remainder of said wall over a length which is substantiallyidentical to the height of the shorter volume 65. The open bottom end 58of the flow duct 57 includes a non-return valve 69 having a ball 70which rests against a seat situated at the top of the valve body 71 andwhich is retained by a transverse bar 72, with all of the components 56,69, 70, 71, and 72 being made of drillable material. Immediately abovethe valve 69, the flow duct 57 includes a zone of weakness 74 forfacilitating breakage thereof by traction after the cement has set.

FIG. 11 shows the casing during cementing. Only the longer main volume64 of the casing has been filled (is in its second state). FIG. 12 showsthe casing after cementing has been completed, but before the cement hasset, with the smaller volume 65 then being filled and put under pressureto press firmly against the enlarged bottom portion 73 of the precedingcasing 52 (which corresponds to the portion 68 of the casing 54 of theinvention).

To implement apparatus of the invention, sections of casing 54 arestored in their first stage folded around a vacuum about the circulationduct 57 and on a reel. To avoid having radiuses of curvature that aretoo small, barium hydroxide or the equivalent is injected into thecasing while it is being evacuated. The barium hydroxide also serves tomake the folded casing heavy so as to combat buoyancy thrust while it isbeing lowered through drilling mud in the borehole. The borehole isprepared for casing and the folded flexible casing is lowered throughthe previously cemented casing 52.

In FIG. 8, the section of casing 54 is located entirely beneath thepreceding casing 52.

In FIGS. 11 and 12, the section of flexible casing ceases to be loweredwhen the shorter top volume 65 is situated level with the enlargedbottom portion 68 or 73 of the preceding casing. To obtain thisarrangement, it is naturally necessary to take the precaution ofinserting the casing so that the volume 65 is at the top thereof. Themain volume 64 is then filled so that it passes from its folded firststate to its inflated second state in which it takes up a rigidcylindrical configuration, and this is done using mud of identicaldensity to the mud in the well to ensure that the section of casing doesnot float. Thereafter a cement slurry is delivered via the duct 57 so asto rise in the annular space 61 between the borehole and the outside ofthe casing. When the slurry reaches the annular gap between the twosections of casing 52 and 65, the shorter length volume 65 is filledwith mud and put under pressure. The wall of this volume is thus pressedfirmly against the inside surface of the bottom end of the precedingcasing, thereby providing autoclaves sealing. Once the cement has set,the duct 57 is withdrawn by traction, thereby breaking it in the zone 74and by increasing the inflation pressure in the volumes 64 and 65 so asto break the weaker portions of their walls, i.e. the ends 55 and 75,and the diaphragm 63. Drilling can then continue using a tool of thesame diameter.

A numerically-worked example of an implementation of the inventionfollows. The borehole may begun directly by drilling at a diameter of81/2" (216 mm) for a final passage of about 6" (152 mm). The filledoutside diameter of a section of casing is then 7" (178 mm), but itsradial section after it has been folded longitudinally under a vacuum isegg-shaped being approximately 53/8" (136 mm) long in one direction and41/4" (108 mm) wide in the other direction. The section of casingincludes an internal circulation duct having a diameter of 2" (51 mm) aspart of a high pressure hose line capable of withstanding the outsidepressure at which the casing is filled. The entire section of casing canthen be stored on a drum which may contain as much as 1,800 meters on adrum that is 4.2 meters in diameter and 2.5 meters long.

The above description relates essentially to an application of theinvention to casing boreholes in the oil industry. In that applicationas in the application of repairing pipework, it may be advantageous toeliminate the outer envelope of the preform. Impregnation resins areavailable that give sufficient coherence to the filamentaryreinforcement for the outer skin to be pointless.

The embodiments described above are given purely by way of non-limitingexample, and other embodiments could be envisaged without going beyondthe ambit of the invention.

I claim:
 1. A tubular preform that is radially deformable between alongitudinally folded state and a substantially cylindrical unfoldedstate to form a length of rigid tube in situ, wherein the preformcomprises a flexible and watertight inner envelope whose peripheralextent is equal to the internal extent of the length of tube, and,formed on the outside of said inner envelope, reinforcement made of astructure comprising a plurality of fibers or strips impregnated with asettable resin, including fibers oriented mainly in the peripheraldirection of the preform, each of these fibers or strips extending overmore than one turn and co-operating with adjacent fibers or strips bymaking contact therewith such that adjacent fibers or strips can slideover one another while the preform is in any state other than itsunfolded state where, under internal pressure, the fibers or strips arelocked together by the friction between them due to a capstan effect. 2.A preform according to claim 1, wherein said structure is constituted bywinding a plurality of long fibers impregnated with settable resin ontothe inner envelope supported by a mandrel and covered with sheets oflongitudinal fibers.
 3. A preform according to claim 1, wherein saidstructure is located between a flexible and watertight inner envelopewhose peripheral extent is equal to the internal extent of the length oftube, and a flexible and watertight outer envelope whose peripheral sizeis equal to the outside size of the length of tube.
 4. A preformaccording to claim 3, wherein said structure is constituted by winding aplurality of sheets of long fibers impregnated with settable resinaround a mandrel covered with the first envelope to make up a thicknessequal to the thickness between the two envelopes.
 5. A preform accordingto claim 3, wherein said structure includes a plurality of concentricsleeves placed one within another, each of the sleeves when under loadhaving a peripheral size that is designed to be slightly larger than thesize of the sleeve it surronds or slightly smaller than the size of thesleeve which surrounds it, thereby forming a compact structure.
 6. Apreform according to claim 3, including a sheet of longitudinal fibersbetween the inner envelope and the structure.
 7. A preform according toclaim 1 wherein the structure is made of a strip of material helicallywound on said inner envelope, said strip having two longitudinal edges,one of which being longer that the other, the structure having multiplelayers with each layer extending from the inner envelope to the outersurface of the structure.
 8. A preform according to claim 3, wherein atleast some of the fibers or strips are made of metal.
 9. A tubularpreform that is radially deformable between a folded state and asubstantially cylindrical unfolded state to form a length of rigid tubein situ, wherein the preform comprises a flexible and watertight innerenvelope whose peripheral extent is equal to the internal extent of thelength of tube, a flexible and watertight outer envelope whoseperipheral size is equal to the outside size of the length of tube, and,confined between the two envelopes, reinforcement made of a structurecomprising a plurality of fibers or strips impregnated with a settableresin, including fibers oriented mainly in the peripheral direction ofthe preform, each fiber or strip extending over more than one turn andco-operating with adjacent fibers or strips by making contact therewithsuch that adjacent fibers or strips can slide over one another while thepreform is in any state other than its unfolded state where, underinternal pressure, the fibers or strips are locked together by thefriction between them due to a capstan effect and wherein, in the foldedstate, it possesses longitudinal edges forming hairpin bends aroundrespective incompressible volumes limiting the radius of curvature offolding.
 10. A preform according to claim 9, wherein each incompressiblevolume is constituted by flexible ducting filled with an incompressiblesubstance.
 11. A tubular preform that is radially deformable between alongitudinally folded state and a substantially cylindrical unfoldedstate to form a length of rigid tube in situ, wherein the preformcomprises a flexible and watertight inner envelope whose peripheralextent is equal to the internal extent of the length of tube, and on theoutside of said inner envelope, reinforcement made of a structurecomprising a plurality of fibers impregnated with a settable resin,including fibers or strips oriented mainly in the peripheral directionof the preform, each of these peripherally-oriented fibers or stripsextending over more than one turn and co-operating with adjacent fibersor strips by making contact therewith such that adjacent fibers orstrips can slide over one another while the preform is in any stateother than its unfolded state where, under internal pressure, the fibersor strips are locked together by the friction between them due to acapstan effect, with the thickness of the filamentary structure beinggreater than 5/10-ths of a millimeter.
 12. A preform according to claim9, for casing a borehole having in folded state a horseshoe shape, withthe two hairpin bends being adjacent each other, such that the largesttransverse dimension of the preform folded in this way is substantiallyless than the inside diameter of the preform in its unfolded state. 13.A preform according to claim 12, including a plurality of peripheralstraps for holding it in the folded state and uniformly distributedalong its length, the breaking strength thereof being designed so thatthey break in succession under the effect of filling pressure movingupwards.
 14. A preform according to claim 13, wherein the space insidethe horseshoe shape constitutes a housing for a material to be used insealing the wall of the tube as provided by the preform when in itsrigid cylindrical state to the wall of the borehole to be cased by saidtube.
 15. A preform according to claim 13, wherein the preform and thesealing material are contained in an envelope that is breakable orelastic, of peripheral size substantially equal to the outsideperipheral size of the preform in its cylindrical state.
 16. A preformaccording to claim 13, including a flexible end wall connected in sealedmanner to one end of the tubular wall and a second flexible end wall atthe opposite end thereof having the filler duct for the tubular sectionpassing therethrough, which duct is connected to a source of fluid underpressure for causing the preform to pass to a cylindrical state from afolded state in which its inside volume is evacuated and kept under avacuum.
 17. A preform according to claim 13, having one end furthestfrom its end through which the filler duct passes which has, when in thecylindrical state, an inside diameter equal to the outside diameter ofits opposite end, and over portions of substantially equal length.
 18. Apreform according to claim 16, wherein the filler duct extends insidethe preform to the vicinity of the opposite end wall.
 19. A preformaccording to claim 18, wherein the duct is connected to two brancheswhich extend in parallel to each other in each of the volumes filledwith incompressible material that limit the above-mentioned foldingradius of curvature, their walls being connected at least in part to thebottom end wall of the preform so as to constitute an extractortherefore after the preform has become rigid and the sealant has set.20. A preform according to claim 8, for forming a length of tube insitu, wherein when in its folded state the preform is in the form of aflap strip.
 21. A method of casing a borehole by means of a preformdeformable between a longitudinally folded state and a substantiallycylindrical unfolded state comprising a flexible and watertight innerenvelope and, formed on the outside of said inner envelope,reinforcement made of a structure comprising a plurality of fibers orstrips impregnated with a settable resin, including fibers orientedmainly in the peripheral direction of the preform, each of these fibersor strips extending over more than one turn and co-operating withadjacent fibers or strips, said preform including a flexible end walland a second flexible end wall at the opposite end thereof having afiller duct passing therethrough, which duct is connected to a source offluid under pressure for causing the preform to pass to a cylindricalstate from a folded state wherein the method comprises the followingsteps:(a) drilling a portion of borehole to a diameter substantiallyequal to the outside diameter of the casing; (b) lowering the foldedsection of flexible preform inside the borehole and then filling it fromthe bottom with a fluid under pressure to bring it into its cylindricalstate starting from the bottom; (c) allowing the resin impregnating thestructure tensioned by the internal pressure to set and allowing theouter sealant to set; (d) raising the filler duct; and (e) repeatingsteps (a) to (d) at a diameter equal to the inside diameter of thepreviously installed length of casing with the descent of the foldedpreform being stopped so that its top portion remains received in thepreviously installed length of casing.
 22. A method of casing accordingto claim 21, by means of said preform having, when in cylindrical state,opposite to the end through which passes the filler duct an end sectionwhose inside diameter is equal to the outside diameter of the other endsection, wherein the method comprises the following steps:(a) drilling aportion of a borehole to a diameter substantially equal to the outsidediameter of the previously installed casing with a bottom portion of theborehole being drilled by means of a reamer to a diameter that isslightly greater than said diameter; (b) lowering the section offlexible preform in its folded state through the previously installedcasing and stopping the lowering of said folded preform so that the topportion of the preform remains received in the previously installedportion of casing whose inside diameter is equal to the outside diameterof the top portion of the preform; (c) filling the preform to bring itfrom its folded state to its cylindrical state, starting from its bottomend; (d) allowing the resin impregnating the filamentary structuretensioned by the internal filling pressure to set and also allowing theexternal sealant to set; and (e) raising the filler duct.
 23. A preformfor casing a borehole wherein said preform is closed at both ends,possesses in a folded first state a maximum outside radial size that isless than the inside diameter it achieves when in an unfolded tubularsecond state, and includes at least one circulation duct extendingaxially inside the preform and passing in sealed manner through itsclosed ends.
 24. A preform according to claim 23, wherein the preform isheld folded into a horseshoe shape by a plurality of encircling bands ofdetermined breaking strength.
 25. A preform according to claim 24,including means for connecting the inside volume of the preform to asource of fluid to cause the preform to pass by inflation from its firststate to its second state, said means being constituted by a separateduct connecting the inside volume of the preform to the source of fluidunder pressure.
 26. A preform according to claim 24, wherein theconnection means is constituted by a branch on the circulation duct andconnected thereto via a branch coupling sleeve.
 27. A preform accordingto claim 24, wherein its inside volume is splitted by a diaphragm intotwo superposed volumes, one of which is short relative to the other. 28.A preform according to claim 27, wherein the longer volume possesses atits end furthest from the other volume, a portion whose length is notless than the length of said other volume and of inside diametersubstantially equal to the outside diameter of said other volume whensaid volumes are in their respective second states.
 29. A preformaccording to claim 28, wherein each of the volumes is fitted withindependent means for connection to a source of fluid under pressure.30. A preform according to claim 27, wherein the ends and the diaphragmare breakable beyond a pressure threshold.
 31. A preform according toclaim 24, wherein said circulation duct includes a non-return valvepreventing fluid from returning towards the source, the non-return valvebeing made of drillable materials.
 32. A preform according to claim 24,wherein the circulation duct includes a disconnection zone situatedinside the section of flexible casing and close to one of its ends. 33.A method of casing a borehole using a preform which is closed at bothends, which possesses in a folded first state a maximum outside radialsize that is less than the inside diameter achieved when in a tubularunfolded second state and which includes at least one circulation ductextending axially inside said preform and passing in sealed mannerthrough its closed ends wherein the method comprises the followingsteps:(a) using a reamer to drill a portion of non-cased borehole havinga diameter greater than the inside diameter of the previously installedcasing; (b) lowering a folded section of preform inside the previouslyinstalled casing and when the entire length of said folded section ofpreform is received inside the installed casing, paying out thecirculation duct so as to place the section of preform beneath thebottom of the previously installed casing; (c) causing sealant liquid toflow via the circulation duct so that the liquid rises in the annulargap between the folded section of preform and the wall of the borehole;(d) filling the section of preform from the bottom with a fluid so as tocause said section of preform to take up its second state; (e) allowingthe preform and the sealant liquid to set, thereby sealing said lengthof casing; and (f) detaching and raising the circulation duct.
 34. Amethod of casing a borehole using a preform which is closed at bothends, which possesses in a folded first state a maximum outside radialsize that is less than the inside diameter achieved when in a tubularunfolded second state and which includes at least one circulation ductextending axially inside said preform and passing in sealed mannerthrough its closed ends, said preform having its inside volume splittedby a diaphragm into two superposed volumes, one of which is shortrelative to the other, the longer volume possessing at its end furthestfrom the other volume, a portion whose length is not less than thelength of said other volume and of inside diameter substantially equalto the outside diameter of said other volume when said volumes are intheir respective second states, wherein the method comprises thefollowing steps:(a) using a reamer to drill a portion of non-casedborehole to a diameter greater than the inside diameter of thepreviously installed casing; (b) lowering the section of preform whilein its first state through the previously installed casing so that itsshort length volume is inserted last; (c) stopping the descent of thefolded section of preform so that its shorter length volume remainsreceived within the previously installed casing; (d) causing sealantliquid to flow along the circulation duct so that the liquid rises upthe annular gap between the portion of the folded section of preform andthe wall of the borehole until it reaches the space between thepreviously installed casing and the shorter volume; (e) filling thelonger volume from the bottom so as to bring it into its second state;(f) filling the shorter volume so as to bring it into its second state;(g) allowing the preform and the sealant liquid to set so as to seal thesection of casing; and (h) detaching and raising the circulation duct.